Serotonin (5-HT) receptors are known to have a plurality of subtypes such as 5-HT1, 5-HT2, 5-HT3 and 5-HT4. These 5-HT4 receptors are disclosed in, for example, European Journal of Pharmacology 146 (1988), 187–188, and Naunyn-Schmiedeberg's Arch. Pharmacol. (1989) 340:403–410.
5-HT4 receptor modulators (e.g., agonists and antagonists) are found to be useful for the treatment of a variety of diseases such as gastroesophageal reflux disease, gastrointestinal disease, gastric motility disorder, non-ulcer dyspepsia, functional dyspepsia, irritable bowel syndrome, constipation, dyspepsia, esophagitis, gastroesophageral disease, nausea, central nervous system disease, alzheimers disease, cognitive disorder, emesis, migraine, neurological disease, pain, and cardiovascular disorders such as cardiac failure and heart arryhthmia (See TiPs, 1992, 13, 141; Ford A. P. D. W. et al., Med. Res. Rev., 1993, 13, 633; Gullikson G. W. et al., Drug Dev. Res., 1992, 26, 405; Richard M. Eglen et al, TiPS, 1995, 16, 391; Bockaert J. Et al., CNS Drugs, 1, 6; Romanelli M. N. et al., Arzheim Forsch./Drug Res., 1993, 43, 913; Kaumann A. et al., Naunyn-Schmiedeberg's. 1991, 344, 150; and Romanelli M. N. et al., Arzheim Forsch./Drug Res., 1993, 43, 913).
A variety of imidazopyridine compounds have been known as 5HT receptor antagonists or agonists. For example, Japanese Patent Publication Laid-Open No. H01-258,674 and H02-643,274 disclose imidazopyridine compounds as 5HT receptor antagonists. WO 96/05166 discloses imidazopyridine compounds as 5HT4 agonists. WO92/15593; U.S. Pat. No. 5,260,303; U.S. Pat. No. 5,604,239; U.S. Pat. No. 5,591,749; U.S. Pat. No. 5,219,850; U.S. Pat. No. 5,434,161; U.S. Pat. No. 5,137,893; U.S. Pat. No. 5,196,547; and EP 504679 describe a variety of imidazopyridine compounds as 5HT3 receptor antagonists. WO94/08998 discloses imidazopyridine compounds as 5HT4 receptor antagonists.
Also, imidazopyridine compounds synthesized for different uses are described in JP2001/6877; WO01/5763; WO 99/50247; WO 97/27852, WO 9738665 and EP 274867.
It would be desirable if there were provided 5HT4 receptor agonists which have more 5HT4 receptor agonist activities.
A variety of imidazopyridine 5-HT4 receptor modulators compounds were disclosed in U.S. Application No. 60/343,371, filed on Oct. 22, 2001. Especially, compounds represented by the following formula is disclosed in U.S. Application No. 60/343,371: 
QT prolongation is known to have a potential liability to produce fatal cardiac arrhythmias of Torsades de Pointes (TdP). The ability to prolong the cardiac action potential duration was identified as being due to an action at the HERG potassium channel. For example, drugs withdrawn from the market due to QT prolongation, such as Cisapride and Terfenadine, are known to be potent HERG potassium channel blocker (Expert Opinion of Pharmacotherapy.; 2, pp. 947–973, 2000). Therefore, it would be desirable if there were provided a novel 5HT4 selective agonist useful for the treatment of a variety of diseases such as gastroesophageal reflux disease, gastrointestinal disease, gastric motility disorder, non-ulcer dyspepsia, functional dyspepsia, irritable bowel syndrome, constipation, dyspepsia, esophagitis, gastroesophageral disease, nausea, central nervous system disease, alzheimers disease, cognitive disorder, emesis, migraine, neurological disease, pain, and cardiovascular disorders such as cardiac failure and heart arrhythmia, by systemic administration and with reduced inhibitory activity at HERG potassium channel.